Internal combustion engines combust an air and fuel mixture to generate drive torque. The combustion process generates exhaust that is exhausted from the engine to atmosphere. The exhaust contains nitrogen oxides (NOx), carbon dioxide (CO2) and carbon monoxide (CO) particulates. An exhaust after-treatment system treats the exhaust to reduce emissions prior to being released to atmosphere.
In an exemplary exhaust after-treatment system, a dosing system injects a dosing agent (e.g., urea) into the exhaust upstream of a catalyst. The exhaust and dosing agent mixture reacts over the catalyst to reduce the level of emissions. The dosing system includes a dosing agent supply and an injector. The amount of dosing agent injected is based on the level of emissions in the exhaust. If the dosing agent supply is empty or at a low level, insufficient dosing agent is injected into the exhaust stream and emissions are not reduced as desired.
It is a concern that vehicle operators may not replenish the required dosing agent. As disclosed in commonly assigned U.S. patent application Ser. No. 11/639,397, filed on Dec. 14, 2006, and entitled “Emissions Conformance For An Exhaust After-Treatment System Having A Dosing Agent Supply”, the disclosure of which is incorporated herein by reference, vehicle operation can enter a limp-home mode that limits the vehicle drivability to encourage the vehicle operator to replenish the dosing agent.